1. Field of the Invention
The present invention is directed to a method for removing color from ionically dyeable polymeric material. The present invention is also directed to a method for extracting dye from ionically dyeable polymeric material. More particularly, the present invention is directed to a method for recycling colored polymeric material which includes contacting the polymeric material with a swelling agent for the material to produce a decolored, ionically dyeable polymeric material and forming an article therefrom.
2. Background
As the amount of available landfill space decreases, and the number of articles manufactured from synthetic polymers increases, there exists an unmet need for environmentally responsible methods for disposal of these polymer containing articles. A welcome alternative to landfill disposal is recycling and reuse of the synthetic polymer material in products which may be the same as or entirely different from the original article.
One significant limitation to the utility of recycled synthetic polymer material is the imparted color. Colorants or dyes are commonly added to virgin polymers for both practical and aesthetic reasons. However, the colorant or dye may significantly impair the processability of or degrade the polymer during conventional recycling processes. Further, the presence of colorant or dye may limit the potential downstream uses of the recycled polymeric material as any color change desired in the downstream use could be limited if not impossible given the original article's color. In a worst case scenario, a article otherwise suitable for recycling would be rejected completely and deposited in a landfill simply because its color is undesirable or inappropriate for a particular downstream use.
Processes for stripping dyes from or decolorizing various materials are well known in the art. For example, U.S. Pat. No. 4,227,881 discloses a process for stripping dyes from textile fabric which includes heating an aqueous solution of an ammonium salt, a sulfite salt and an organic sulfonate to at least 140.degree. F. (60.degree. C.) and adding the dyed fabric to the heated solution while maintaining the temperature of the solution. In addition to the costly heating and temperature maintenance step, this process has the drawback of producing fabrics which after processing exhibit a remaining color depth. In U.S. Pat. No. 4,783,193 a process for stripping color from synthetic polymer products by contacting the colored polymer with a chemical system is disclosed. The described process uses unstable dispersions of alkyl halides and aqueous solutions of bleaching/oxidizing agents to which specified quantities of acids and surfactant/wetting agents are added. Among the drawbacks are the use of potentially hazardous halogens and the special provisions required to prevent escape of vapors which could cause environmental harm. Further, the use of the chemical system may restrict or eliminate the polymeric materials recyclability. In general, processes which utilize harsh stripping agents destroy the usefulness of the colorant thus generating a chemical waste stream that must be treated or disposed of in an environmentally conscious manner. These methods can also generate unremovable colorant fragments which limit the downstream recycleability and utility of the color-stripped material.
Thus an unmet need exists for a cost-effective and environmentally friendly process for removing color from synthetic polymer materials which completely removes the colorant from the material without degrading or otherwise decreasing the material's or the colorant's availability for recycling and re-use.